Iran has been sanctioned before, and was expecting these. It
is better prepared than people realize.

Oil is important to Iran, but it is not everything. It
is "large regional economy with a relatively diversified
structure".

Other nations (North Korea, Cuba) have dealt with harsher
sanctions for larger periods.

Iran has options for its oil, it can enter barter
arrangements, sell at a discount, or conduct transactions in
other currencies, as it has in India.

The sanctions have worsened problems in the Iranian economy,
including inflation/high staple prices and unemployment. However,
these problems primarily affect ordinary Iranians. The impact on
the ruling elite is muted.

Iran's oil revenues have allowed it to build currency
reserves of at least $80 billion. They aren't in danger of being
unable to import essential goods in the near term.

Hopefully the talks will succeed. There have been promising
signs, but Iran may be capable of surviving sanctions for some
time to come.